Device properties and degradation mechanisms of organic light-emitting diodes composed of organic layers with orientation polarization

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Findings of this study are as follows : 1) Several polar molecules that are commonly used in organic semiconductor devices spontaneously forms orientation polarization in their evaporated films. 2) The origin of interface charge at organic hetero interfaces is polarization charge originating from the orientation polarization. 3) Presence of polar molecules in the vicinity of organic hetero interface suppresses charge dispersion. 4) Light irradiation during the film formation of a polar molecule changes the charge accumulation property in the resultant devices, and causes a shorter lifetime. These findings indicate that permanent dipole moment is an important parameter that strongly affects on the device properties of organic semiconductor devices.